1) Field of the Invention
The present invention relates to the production of synthetic polymeric material in filament form for use in fiber manufacture and, more particularly, to apparatus and method for drawing, heat setting, and crimping such filamentary material, particularly polyethylene terephthalate (PET) commonly referred to as polyester. In particular, the present invention relates to a new draw line for tow having an undrawn denier of about 3 million or greater and a drawn tow having a denier of 1.0 million denier or greater. More specifically, the present invention relates to drawing, heat setting and crimping of a polymeric tow, whereby the tow has a constant denier per inch of width after drawing.
2) Prior Art
In the conventional manufacture of synthetic yarns, a molten polymeric material is extruded in the form of multiple continuous filaments which, after quenching to cool the filaments, are gathered and transported longitudinally in a lengthwise co-extensive bundle commonly referred to as a tow. Particularly with polymeric materials such as PET, the tows are subjected to a subsequent drawing and heating operation to orient and heat set the molecular structure of each constituent filament in each tow.
A typical drawing and heat setting operation involves transporting multiple tows in side-by-side relation sequentially through two or more drawstands operating at progressively greater driven speeds to exert a lengthwise stretching force on the tows and their individual filaments while traveling between the drawstands thereby performing a drawing to molecularly orient the individual filaments, followed by a calender structure about which the tow travels peripherally in a sinuous path to be sufficiently heated to set the molecular orientation of the filaments. Normally, the tow is transported through a quench stand to be cooled immediately following the calender structure and finally a number of tows are combined together in a stacker and transported to a crimper, such as a so called stuffer box, to impart texture and bulk to the filaments.
Conventional draw-line-stands spread out the tow in a ribbon-like shape before drawing the filaments of the tow and the flattened tow is not recombined until after quenching and before the crimper. Conventional draw-line-stands employ cantilevered rolls for the drawing operation of the ribbon-like tow, which requires the supporting walls to be very large, and the mechanical bearing structures of the cantilevered rolls to be sufficiently massive to support the rolls and resist the bending moments and deflective forces imposed by tows of the size and denier conventionally being processed.
U.S. Pat. No. 2,918,346 to Paulsen discloses a process for orienting a dense tow of polyester filaments. Paulsen discloses heating the tow band in a heated bath and drawing the tow 2.3 to 5.8 times its original length. In Example 3, Paulsen discloses an undrawn tow having a density of 142,000 denier per inch, corresponding to a drawn density between about 24,000 and 62,000 denier per inch.
U.S. Pat. No. 3,259,681 to Bull et al. schematically illustrates a process for making polyester tow starting from the spinnerette and continuing, through the drawing stages, heat setting, and lastly crimping of the tow. In Example 4 of this patent an undrawn tow of 130,000 denier per inch is disclosed.
U.S. Pat. No. 3,567,817 to Spiller discloses a process for drawing a tow by means of a series of rolls, including hot liquid to heat the tow between draws. In Example 4 of this patent,an undrawn polyester tow of approximately 267,000 denier per inch is disclosed.
While the patents to Paulsen, Bull et al. and Spiller disclose large denier tows, these are undrawn. The present invention produces drawn tows of 150,000 denier/inch or greater.
Tow drawing and heat setting lines of the type described above have proven to be reasonably effective and reliable for the intended purpose. However, as the fiber industry continually strives to improve efficiency and reduce manufacturing costs, much effort has been devoted to attempts to increase the number of filaments in each tow and to increase the lineal speed at which the filaments are processed through the drawing and heat setting line, which presents particular difficulties and problems in construction of the apparatus within the line and in effectively accomplishing heat setting of all of the constituent filaments in a tow.